“Information terminal which is hardly broken, light in weight and inexpensive” which any one can use at any place has been recently required. In order to realize this, the use of a material which has cost benefit and is soft is desired in a transistor which is a key device (the most important element) of information terminal. However, an inorganic material such as silicon which has been conventionally used can not sufficiently meet such demand.
Due to such a condition, “an organic transistor (OFET)” using an organic compound having semiconductor characteristics, which is called an organic semiconductor, in an active part (a semiconductor layer) of the transistor has been the focus of attention (refer to NPL 1). Such the organic semiconductor is soft and is capable of treating at low temperature, and an affinity for a solvent is generally high. Therefore, there is an advantage that the semiconductor layer can be manufactured (film-deposited) on a plastic substrate which is flexible by using a wet process such as coating or printing at a low cost, and the organic semiconductor is expected as a next-generation material for electronic element which is essential for a realization of “information terminal which is hardly broken, light in weight and inexpensive”.
Phthalocyanines are one of the typical organic semiconductors, and it is known that excellent transistor characteristics are exhibited by controlling a higher-order structure, that is, an arrangement and an aggregation state of molecules (refer to NPL 2). However, since phthalocyanines have low solvent solubility, it is difficult to produce an element by the wet process, therefore, when phthalocyanines are used for an electronic element, a dry process such as vacuum evaporation or sputtering is generally used. Since such the dry process is a complicated and expensive process, it becomes difficult to provide a low cost electronic element which is one of characteristics of the organic semiconductor.
In order to solve the problem, a technology which manufactures a transistor by the wet process by introducing a solubilizing substituent into phthalocyanines and enhancing the solvent solubility, is also disclosed (refer to PTL 1). However, in the method, since each molecule of phthalocyanines is not sufficiently arranged and the higher-order structure can not be controlled, transistor characteristics are inferior, as compared with a transistor by a dry process. In order to exhibit excellent semiconductor characteristics, it is important that each molecule has a crystal structure having dimensionality in which each molecule arranges in a certain direction; therefore, there is an expectation in a wire- or rod-like one-dimensional crystalline structure (a crystalline structure having a major axis (a long axis) and a minor axis (a short axis)).
On the other hand, in order to more favorably apply them toward the electronic element in which the production by the wet process is expected, the above one-dimensional crystalline structure is a one-dimensional crystalline structure in which the minor axis is preferably 500 nm or less (hereinafter, written as a nano-sized one-dimensional substance).
Phthalocyanines are widely used as a coloring agent for paint in a printing ink, and many technologies which control the crystal size or the shape thereof are also known. For example, there are a solvent salt milling method of mixing an inorganic salt and an organic solvent with a metal phthalocyanine and finely grinding and micronizing pigments by using a grinding device (for example, refer to PTL 2), a crystallization method of settling out the above metal phthalocyanine in a large quantity of water after it is dissolved in sulfuric acid (for example, refer to PTL 3), and the like. However, even using these methods, it was difficult to obtain the nano-sized substance composed of phthalocyanines as described above.
On the other hand, the present inventors disclose a technology of manufacturing a device by a wet process using the phthalocyanine nanowire which is produced using unsubstituted phthalocyanine and phthalocyanine having a substituent (refer to PTLS 4, 5 and 6). However, it is difficult to say that the above phthalocyanine nanowire is completely optimized in a performance aspect.